'I nearly choked when I saw the email that invited me,' she told the Telegraph. 'I didn’t really sleep the night before,' she says of her first day on set, 'It was exciting – and frightening. The first moment of sitting in this incredible group of actors – who have been in our sitting room so often... I remember the cold of the day, the big coats they gave us. And the great hallway at Highclere where I sang – amazing acoustics!'

The appearance comes before Te Kanawa’s Royal Opera return as the Duchess de Crackentorp in Donizetti's uproarious comedy La Fille du régiment later this Season. The role has been expanded for the forthcoming revival to include some singing, marking Te Kanawa’s first performance at Covent Garden since 1997.

The episode of Downton Abbey will be broadcast on ITV at 9pm on Sunday 6 October.